Polymer electrolyte fuel cells operate at low temperatures around 80° C. Accordingly, if a hydrogen-rich gas serving as fuel contains a certain or higher level of carbon monoxide, the platinum anode catalyst may be CO-poisoned, which may reduce the power generation performance and ultimately disable the fuel cell from generating power.
Home-use polymer electrolyte fuel cell power generation systems convert a town gas, LP gas, kerosene, or the like into a hydrogen-rich gas using a fuel reformer and use this hydrogen-rich gas as fuel. To avoid CO poisoning as described above, these systems preferably always control the CO concentration of the fuel cell anode inlet gas to 10 ppm or less. In the final stage of the fuel reforming process, many of the actual systems use a selective CO oxidation catalyst, which mixes air into the generated gas and oxidizes CO in the gas into CO2.CO+½O2═CO2  Reaction Formula 1
However, as shown in Reaction Formula 1, such a catalyst must usually take in air from outside. Accordingly, the fuel reformer must be provided with an air blower and a control system thereof, and a complicated gas mixing structure for uniformly mixing supplied air into the reaction gas.
Currently, selective CO methanation catalysts are attracting attention as a new approach to replace selective CO oxidation catalysts (e.g., Patent Literature 1 and 2).
Patent Literature 1 discloses a selective CO methanation catalyst prepared by impregnating, with ruthenium salt, a nonstoichiometric Ni—Al complex oxide precursor prepared by plasma spray and performing reduction treatment. This selective CO methanation catalyst can selectively methanize CO even at high temperatures, at which a CO2 methanation reaction and a reverse water-gas shift reaction proceed more dominantly than a CO methanation reaction over traditional catalysts.
Patent Literature 2 discloses a selective CO methanation catalyst whose active component adsorbs or couples with at least one selected from halogen, inorganic acid, and metal oxygen acid serving as carbon dioxide reaction inhibitors. This selective CO methanation catalyst is excellent at selecting a CO methanation reaction